Dear Referee 3,
thank you for reviewing our article. Your remarks will help a lot to improve this article. You
raised important questions, which we will try to answer in the point-by point replies below.
Specific comments:
Pag. 2950, line 26: ’As the glide-snow avalanche model includes the important role of
ground roughness – which is strongly influenced by the vegetation cover – we
are able to quantify the friction of the ground cover of our test site’. Formulation?
I think you link the ground roughness of your test site to the coulomb friction which
is employed in the model.
>> We will change the sentence to ‘As the glide-snow avalanche model includes the
important role of ground roughness – which is strongly influenced by the vegetation cover –
we are able to link the observed terrain roughness and ground vegetation to specific
Coulomb friction values’.
(2951, 20 ’.... Release height was estimated with the snow height hs measured at
the meteorological station in Davos. Generally, how is your snow height defined
(slope normal or in direction of gravity?)? Why is the station data representative
for all of your release areas? This is important, e.g. for 2952, 23 This allowed us
to relate the observed heights to the calculated friction parameter. How did you
exactly determine lg / distinguish between slab / stauchwall / (entrained) snow in
the path (I think it is hard to define the end of a slab for a ground avalanche after
release (even with time laps photography)?. What about days with bad visibility?.
>> We changed ‘snow height’ (perpendicular) to ‘snow depth’ (vertical) throughout the
paper according to the European Avalanche Glossary,
http://www.avalanches.org/en/includes/glossary/glossary_en_all.html#n106. See also
comments to referee 1. Snow depth was measured in Davos (1560 m.a.s.l.) and on the
Dorfberg on an elevation of 2150 m.a.s.l. We analysed both datasets to find a relationship
between snow depth, slope angle and slab length. The correlation was only weak for slab
length (R2=0,11; see figure 8) and no correlation between snow depth and slope angle was
found. The snow depth at the Dorfberg station was always between 20 and 60 cm higher
than in Davos. But the result of our analysis was similar: no clear correlation. We chose the
data from Davos because the snow depth in the release areas was smaller than on the flat
field station on the Dorfberg. The release areas were all exposed to the sun, therefore we
assume the measurements from Davos to be closer to reality. Of course there is an
uncertainty, but we assume the measured snow depths to be representative, at least for our
qualitative results.
You mention page 2952, line 23 in this context. In this paragraph we talk about terrain height
ht and vegetation height hv, not about snow depth hs. Maybe this is clearer now, that we
changed ‘snow height’ to ‘snow depth’.
The definition of the release length lg was precise as the stauchwall is fixed to the ground
and a rest of snow stays fixed, even after release. The release areas without snow (brown
underlying surface) were always clearly distinguishable. You are right, that an exact
definition of the stauchwall area was hardly possible, therefore we followed observations,
that the stauchwall length ls is approximately twice the snow depth hs (page 2958, line 25).
On days with bad visibility the first visible picture of the slope was used to document the
release areas. All avalanches were documented within a few hours after release.
Page 2952, 0 ’Segregation of avalanches’ Formulation.
>> See comment to reviewer2: we will replace segregation with selection.
2953, 6 ’... Several events without stauchwall were neglected in further studies...’. Generally,
do all events correspond to different locations or are there also multiple events (maybe with
different slab length) at the same location? However, i do not see the relevance of the 10167=34 avalanches for this paper.
>> There were also some events at the same locations with different slab lengths and extent
at different times.
We draw general conclusions from all avalanche events concerning the main vegetation and
terrain types and their specific heights (section 3.1). More events lead thereby to stronger
statements. For our comparison of avalanche events with model calculations we could only
use cases with stauchwall (section 3.3). Therefore we made this distinction.
2954, 4 ’m = ρ lm’ Should this not rather be mass per unit width and thus be
m = ρ h lm, compare also Bartelt et al. 2012. This is very important for your hs
evaluation.
>> You are right here; the formula should be: m = ρ hs cosα lm. We will change that.
2954, 14 ’When the interface balances the lost tensile force, it is seen as an
increase in the friction μ’. Formulation?
>> We will delete this sentence, because it is a repetition of line 7. We will include ‘μm’ in line
9 to clarify the denotation.
2955, 1 ’The model predicts the total strain..’ This formulation is not clear to me.
The relation of u and ε is another (important) constraint!?
>> We will change the sentence to: ‘The model predicts the strain rate ε = u/2ls in the
stauchwall. The total strain Ɛ and therefore total deformation is calculated by summing the
strain-rates at every calculation step with length ∆t:
Ɛ(t+∆𝑡)= ε(t) + ε * ∆t‘
2955, 2 ’When the strain-rates exceed a critical value, we consider the stauchwall
to fail and an avalanche is released.’ This is a very important point/assumption
and should be highlighted (earlier).
>> We will include ‘The avalanche releases if a critical strain-rate is reached.’ in line 7 on
page 2954.
2956, 4 ’In the model calculations we tested different snow types and snow
heights to investigate the role these parameters had on glide-snow avalanche
formation.’ Did you? I see that you varied density and height, which have an
influence on the strain rate (and maybe then on the formation).
>> Good point. We will change the sentence to ’In the model calculations we tested different
snow densities and snow depths to investigate the role these parameters had on strain-rates
and therefore glide-snow avalanche formation.’
2956, 10 ’Most releases in the Dorfberg study area where found on long grass
(45 avalanches) and on low dwarf shrub vegetation (49 avalanches)..’ It would be
more important how many of your 67 avalanches (which are actually important
for the model comparison) are in which category.
>> This is a general observation and we think it is important to mention the total number.
We will include a sentence in line 11 on page 2953: ‘Of these 67 events 31 released on
compacted long grass, 4 on upright short grass, 31 on low dwarf shrubs and one on strong
lignified shrubs.’
2957, 18 ’Snow height hs (at the release) correlated only weakly’ How do you determine the
correlation?
>> In the caption of Fig. 8 the coefficient of correlation is written (R2=0.11).
2958, 1 ’stauchwall strength...’ You mean strain rate? What are your ranges for
lm, α and μ?
>> Yes, strain rate, we will change ‘stauchwall strength’ to ‘strain rate’. The range of μ is
written in line 10 on the same page (0.33 < μ < 0.81). The tested slab lengths lm (30m, 40m,
50m, 60m) and slope angles (30°, 35°, 40°, 45°) are clearly depicted in Fig. 8.
2958, 6 ’We kept the material parameters...’ You should tell what values (and why!) you kept
your material parameters constants. A short motivation why these values (and even the
employed model) are chosen would be nice.
>> You are right! We will include the sentence ‘The material parameters and the critical
strain rate were defined according to the work of Von Moos et al. (2003), Scapozza (2003)
and Bartelt et al. (2012).’ and include the values of the material parameters in line 6 (Em =
1.5*108, Ek = 1.5*107, ηm = 1.4*109, ηk = 2.5*106). These values are typical for snow
densities of around ρ= 250 kg/m3.
2958, 25 ’The pressure on the stauchwall also depends on snow depth hs’ Is pressure the
correct term? If height of snowcover and stauchwall are the same, results should be invariant
to changes of the snow height (Bartelt et al. 2012). In this context see my comment above.
>> Results are not invariant to changes in snow depth. The mass of snow m depends on the
snow depth. What we want to stress here is, that variations in snow depth have only a small
influence on model results which is an important result. Glide-snow avalanches release
almost independently of the snow height. The temperature of the snow-soil interface (meltwater accumulation) and ground friction are much more important parameters. Snow depth
influences the compaction of shrubs and other large growing vegetation and therefore
maybe has an influence on the ground friction but we did not find a clear correlation.
2959, 15 ’Friction values between..’ Is this your model μ or a guideline μ ? Or
are the μ employed in the same mechanical model? If not, you should include a
description of the guideline model and watch your different μi.
>> We will follow your suggestion here and include a short description of the model used for
the guidelines in Switzerland in line 7 on page 2950. The μ is defined as ‘angle of friction’ in
the guidelines. We will denote this μ with μd to account for the different usage and the
model ‘µ’ to ‘µm’throughout the paper.
2959, 16 ’Observed terrain categories which are below stauchwall model calculation
curves in Fig. 10 indicate lower ground friction than calculated.’ Below what?
Please specify.
>> We will change the sentence to ’A lower ground friction of the observed events is
indicated if the length lm + ls of the three terrain and vegetation categories is lower than the
model calculation curves in Fig. 10’. We hope this is clearer now.
2959, 28 ’...assume friction parameter ... ’ See comment above, is this really the
same model / _? Provide more details on your employed guideline models (e.g.
2949, 21 – 2950, 8). You plot them anyways in your figures.
>> see comment above.
2961, 5’..predicts failure or resistance depending on the slab length, snow height,
snow density and ground roughness...’ Formulation? Ground roughness is not a
model parameter.
>> We will replace the expression ‘ground roughness‘ with ‘basal friction‘.
2961, 6 ’We defined a critical strain rate which in turn defines the maximum slab
length and slope angle allowable to prevent glide-snow avalanche release.’ This
is very important and should be stated earlier in more detail.
>> See comment above.
2961, 8’...The model results...’ You should also state that you did not test for the
other model parameters (elasticity E and viscosity η)
>> We will include a sentence stating that: ‘The material parameters elasticity Em, Ek and
viscosity ηm, ηk were kept constant.’
Fig. 1: For a better understanding of the paper it would be helpful to include your
different l measures in this picture.
>> We will follow your suggestion and include lg and ls here.
Fig. 8: You should state what correlation measure R2 is.
>> We will include ‘coefficient of correlation’ to clarify that.
Fig. 9: Is this really the dependency of μ on lm and α or rather combinations of the three that
lead to a strain rate ε greater than your critical value?, see also 2956 2 ’Different friction
parameters μ were applied in the model calculations. By comparison we could quantify the
friction values we observed in the field.’
>> We will include ‘…for a critical strain rate ε = 0.01’ in the first sentence.
Fig. 10: The colors (yellow, light and dark green) are a bit hard to distinguish, maybe different
colors and symbols would help?
>> see reply to reviewer 1. We will change the colors and symbols.